Surface hardening of metal body consisting of or containing titanium or zirconium



United States Patent SURFACE HARDENING 0F METAL BODY (ISN- SlSTlNG OF OR CONTAINENG TITANIUM 0R ZKRCONIUM Zenichiro Takao, Nishinomiya, and Shigeo Inomata and Koiehi Nakano, Higashinada-ku, Kobe, Japan, assignors to Kobe Steel Works, Ltd, Kobe, Japan No Drawing. Filed Aug. 1, 1966, Ser. No. 46,351

4 Claims. (Cl. 148-131) The present invention relates to surface hardened metal bodies or articles consisting of or containing titanium or zirconium, and also to a process for surface hardening metal bodies or articlesconsisting of or containing titanium or zirconium.

The metals belonging to the titanium group of the periodic system, particularly titanium, zirconium and alloys containing the same have relatively low specific gravities and are excellent in tensile strength and anticorrosive properties, and therefore have extensively been used as materials for various articles, structures, apparatus, etc. including chemical apparatus and appliances. However,. titanium and zirconium are low in hardness and are poor in wear resistance and furthermore have rawbacks that they are damaged particularly when applied to those which are subjected to friction. For these reasons, these materials are not fully satisfactory in spite of their various excellent properties.

It is an object of the present invention to provide surface hardened metal bodies or articles consisting of or containing titanium or zirconium which show excellent wear resistance and antifriction due to the hardened surface layer.

It is another object of the present invention to provide a process for surface hardening metal bodies or articles consisting of or containing titanium or zirconium to render them wear resistant and antifrictive to make them more useful.

In accordance with the invention, an improved metal body or article consists of a base metal consisting of or containing titanium or zirconium and a surface hardened coating or layer which consists of the nitride and/ or oxide of the metal or alloy of the said base, or consists of a dispersed layer of the nitride and/ or oxide.

The hardened surface coating or layer is formed by reacting the surface layer of the base metal or alloy with oxygen and/ or nitrogen. It is preferable to use gaseous oxygen and gaseous nitrogen as oxidizing and nitridation agents respectively. More particularly, according to the present invention, the nitride and/ or oxide are formed by utilizing the so-called inert gas shielded arc welding arrangement with or without a filler metal rod consisting of the same material as the base metal or alloy. Oxygen and/ or nitrogen gas are mixed with the inert gas so that the nitridation and/or oxidation occur While the surface is being covered by the inert gas. When the filler metal is not used the surface of the base is reacted with oxygen and/or nitrogen to integrally form the oxide and/ or nitride thereon, while when the filler metal is used the molten filler metal itself forms the oxide and/or nitride layer or coating on the base.

Titanium is chemically stable below 500 C. but becomes very active at higher temperatures and reacts with oxygen at temperatures higher than the red heat (500 C.) to form titanium oxide as a solid solution or dispersion layer consisting mainly of titanium dioxide, and reacts with nitrogen at temperatures higher than 800 C. to form a solid solution or dispersion layer of titanium nitride. In this connection it should be noted that solubility of oxygen and nitrogen in titanium is appreciably higher than in other practical metals. Similarly, zirconium reacts with oxygen and nitrogen at elevated temperatures (500 C.). The same is true in respect to titanium or zirconium base alloys. In any case, the oxide and/ or nitride forms very hard surface layer or coating on the base metal or alloy.

According to the present invention, the formation of the desired oxide and/or nitride is effected by shielding the surface of the base metal body or article with an inert gas such as argon or helium and the surface is are molten or coated with additional molten metal (by using a filler metal rod) while introducing a predetermined amount of oxygen and/or nitrogen in the inert gas.

As is known, atmospheric air is abundant with oxygen and nitrogen and it is apparent that when air is employed oxygen and nitrogen as contained therein serve as reactive gas to form the oxide and nitride. Simply considered, the use of atmospheric air may be convenient and economical. However, it has been found that the same is not true from the practical point of view. That is, the flow of air into the reaction zone is very unstable and nonuniform and in addition thereto are producing condition such as electric current is not constant at all times and usually varies from instant to instant, so that the formed oxide and nitride are nonuniform in the extent and structure.

Therefore, according to the invention it is preferable not to use atmospheric air but to introduce into the inert gas separately prepared oxygen and/or nitrogen. Thus, the amount and proportions of oxygen and/or nitrogen can be controlled quite easily as desired to stabilize the oxidation and/or nitridation reaction and form the desired and uniform hardened surface.

As mentioned hereinbefore, it is preferable to employ an inert gas shielded arc welding arrangement which, so well known to those skilled in the art as requiring no detailed explanation, is a shield arc welding carried out in an inert gaseous atmosphere. As is conventional, an electrode of material having a high melting point such as tungsten is employed. When the hardened layer to be formed is relatively thin A mm. or less), no filler metal rod is used and the surface to be hardened is are molten and reacted with oxygen and/or nitrogen While shielded with the inert gas to form the hard oxide and/or nitride. If the hardened layer to be formed is relatively thick (up to 5 mm. or thicker), it is preferable to use a filler metal in the usual manner. The filler metal which is the same material as the base metal to be coated is similarly arc molten and reacted with oxygen and/ or nitrogen while shielded with the inert gas to form the hard oxide and/ or nitride which are deposited on the said surface.

It is apparent that the amount of oxygen and/ or nitrogen to be supplied in the inert gas will largely control the hardness of the formed layer or coating. Thus, when the amount of the reactive gas is less than that required no sufiicient hardness would be obtained, while if the amount of the reactive gas is excessive fragility of the oxide and/ or nitride is unduly increased so that the surface would become brittle.

The amount of the reactive gas is selected depending upon the desired hardness to be accomplished, the particular metal or alloy from which the body or article is formed, and the thickness of the hardened layer or coating. This amount can be selected easily by those skilled in the art by means of a small scale pretesting. The amount of the reactive gas (oxygen and/ or nitrogen) is determined by the proportion occupying in the inert gas. Generally, when the metal surface itself is molten and hardened without using a metal deposition from the filler met-a1 rod it has been found that the amount of the reactive gas is preferable to be selected less than 15% by volume of the inert gas, while when the metal deposition is used the amount of the reactive gas is preferable to be less than 10% by volume of the inert gas. In the latter case the said less amount is caused by the use of 45 cording to gas analysis. In any case, the Welding conditions were equally' as follows:

the filler metal rod for the deposition coating. That is, Welding current 75 95 amp when such filler metal rod is employed atmospheric air Arc Voltage comes to get mixed in even if the inert gas shield is es- Arclength mm t'ablished, and oxygen and nitrogen contained in this air Gas HOW 15 ft s/hr.

would take part in the reaction so that this must be taken Welding speed 100430 {mm/mil into consideration beforehand.

Generally the Weld or are current is f bl to be In each case the depositioncoa-tlng or layer was formed controlled within the range from 60 to 130 amp., alh thickness of 5 and lts hardhes rt*Thhrkahly though not absolutely necessary to be limited to this parhlghef than that of the base mhtal tltahlu'mticul ar range. The arc length usually is about 2-10 mm. Example 2 7 l 0 I v 2 3 .5; z 3 2 2 3 dhehum s f: In 'th1s example, bodies of titan um, trtanlum base ale 1 6 gas a or e aroun e loys, zirconium, and zirconium base alloys were surface portion to be wgelded or molten may, 1n most cases, be hardened by amploying an oxygen and/o1. nitmgm gas i g; g d 1 1 mixed inert gas shielded arc welding arrangement with- 1 a d ip 6 so ayer or if out using a filler metal, under various conditions. The $2 3? g ifii i coatmg zf 0n results were as indicated in the fol-lowing table. In any 6 me i o y or m e 15 very um Orm an i y case, the surface hardness was measured by Vickers hardhas hardness of from 250 to 550 as measured by V1cxers t k 1 n ness meter (load 30 gs.). hardness meter (load 30 rigs).

According to this invention, since the reactive gas (oxy- W 1d A A a R W m gen and/ or nitrogen) is introduced in the inert gas which Body g @33 gg f Speeed su face creates an inert gas shield the stability and uniformity of ng (mm) (In /hr.) percent g'liglj/ hardness the reaction are assured, the control of the reaction is (a easy so that there 1s obtained a umform hard layer or Ti H50 H0 1O 30 (02) 10mm 2504300 coating. By llSlIlg the filler metal rod for deposiuon a Ti al10y 00-150 2-10 10-g0 30 282) 100-150 25 -200 r .1 t z. Zr 00-180 2-10 10- 0 0 00-150 25 00 tlnch coatmg, if desired, can be obta ned. In th s case, by Zr (H80 H0 10 30 g 100450 25mm controlling the amount of the deposition, the thickness of the hard coating may be varied as desired. Furthermore, 30 Example 3 since the definite or calculated amount of oxygen and/ or T I d an b a nitrogen can be introduced, and undesired intrusion of b a 15 i fi g i i atmospheric air (which would cause nonuniformity of the 165 ace ar e e y W 051.1 g a 1 minim formed 1a er or 60min is v revented b the inert as oxide and n1tr1de layer thereon. A usual mert gw shieldd th a n 35 ed arc Welding apparatus with tungsten elec rode was S 1 Z e ayel or coa Hg mime 18 i an y employed together with a filler metal rod as indicated for form in hardness and structure or composruon. the deposition The Tesuh was as follows:

The invention will be further described with reference v a to the following examples. However, 1t should be under W61 d Are Argon Reactive stood that these examples are for illustration only and not 40 Body curlength g as gas, Filler Surface for limiting the invention in any way. 53 (mm) (ft/hr) percent metal hardness Example 1 Ti 00-150 g-io 10-3 (81) T T1i1 300-2 0 A titanium rod circular in cross section and 17 mm. gig 5;: 23328 :18 18:2 20 13 35 28: in diameter was surface hardened by depositing a tita- Tialloyn 69450 10-30 20 (O2) Timmy 3OO'5OO nium oxide layer thereon. A usual inert gas shielded are welding apparatus with tungsten electrode was employed In y Case, the Welthhg Speed was 109150 mill/mmtogether with a filler titanium rod for the deposition. In E m l 4 the first Weld deposmcn was earned out by using In this example, various titanium, zirconium and their usual or Common argon gas (Oxygen Fontent 0% N base alloy bodies listed below were surface hardened by the fiamfi Pfocfiddte Was ffipeated with the of stgma employing an oxygen and/ or nitrogen gas mixed inert gas grade argon gas y cohtil'lt 5% and finally 'Wlth a shielded arc welding with or without using a filler metal, mixture of equal amount of argon gas and sigma grade under various conditions indicated. The various condigas, the oxygen content in said mixture being 3.4% actions and results are given below.

Reactive Gas, Weld Shield Percent Current Gas flow Speed Length Exp. Body Filler Rod gas (amp.) (l./1nin.) (111111.! of arc min.) (mm.)

1 0 100-130 5-10 100-130 34 3 0 100-130 5-10 100-130 34 0 0 100-130 5-10 100-130 3-4 0 1 100-130 5-10 100-130 34 0 3 100-130 5-10 100-130 34 0 5 100-130 5-10 100-130 3-4 Ti 0 10 100-130 51-10 100-130 3-4 Ti alloy--- 2 0 100-130 5-10 30-120 5-3 Ti alloy". 2 0 100-130 5-10 30-120 5-3 5 0 100-120 5-10 100-130 3-4 0 5 100-120 5-10 100-130 3-4 5 0 100-120 7 100-130 3-4 3 0 90130 7 100-120 3-4 0 0 -130 7 -120 3-4 0 1 90-130 7 100-120 3-1 0 0 90-130 7 100-120 3-4 0 10 90-130 7 100-120 3-4 5 0 00-120 7 100-120 34 0 0 30-120 7 100-120 3-5 In the above table, the alloy of Exp. 8 consisted of 0.025% C, 0.065% Fe, 0.05% Si, 1.06% Mo, 4.53% Al, 2% Cr and rest Ti, while the alloy of Exp. 9 consisted of 0.2% C, 0.075% Fe, 0.015% Si, 4.36% Al, 4.54% Mn and rest Ti.

After the welding operation, hardness of these metal bodies was as indicated below, when measured by Vickers hardness meter (load 30 kgs.).

Exp. No.: Hardness 1 300-350 2 350-460 3 400-550 4 320-350 5 300-400 6 350-480 7 470-550 8 370-450 9 390-510 10 400-550 11 450-550 1.. 400-550 13 350-400 14 350-450 15 250-300 16 300-420 17 350-500 18 350-400 19 200-250 What we claim is:

1. A method of surface-hardening a metal body selected from the group consisting of titanium and zirconium, which comprises the steps of: forming a layer on the surface of the body by reacting said body with a reactive gaseous element in an inert gas-shielded arc welding arrangement by heating the body surface to a temperate at which it is molten, and introducing in the inert gas the reactive gaseous element so that said surface of the body while being arc-welded and shielded by the inert gas, is reacted with said reactive gaseous element to form the layer.

2. A method of surface hardening a metal body selected from the group consisting of titanium, zirconium, and titanium base alloys, said method comprising the steps of: shielding the body with an inert gas having mixed therewith a measured amount of reactive gas for reacting with the body and simultaneously arc welding the body in the gas shield at a temperature which provides a molten surface on said body so that the molten portion of the body reacts with the reactive gas to form a hard layer on the surface of said body.

3. A method of surface hardening a metal body selected from the group consisting of titanium, Zirconium, an alloy of 0.025% C, 0.065% Fe, 0.05% Si, 1.06% Mo, 4.53% Al, 2% Cr and the remainder titanium, and an alloy of 0.2% C, 0.075% Fe, 0.015% Si, 4.36% A1, 4.5% Mn and the remainder titanium, said method comprising the steps of shielding the body with an inert gas selected from the group consisting of argon and helium, and having mixed therewith a measured amount of reactive gas selected from the group consisting of oxygen and nitrogen for reacting with the body to thereby form a hard oxide and/or nitride layer, said inert gas being supplied at a rate of 10-30 ft. per hour and simultaneously arc welding the body in the gas shield at a temperature which provides a molten surface on said body so that the molten portion of the body reacts with the reactive gas to form a hard layer on the surface of said body.

4. A method as defined in claim 3 comprising depositing metal from a filler metal rod onto the body during arc welding.

References Cited in the file of this patent UNITED STATES PATENTS 1,748,378 Armstrong Feb. 25, 1930 2,523,883 Strauchen et a1 Sept. 26, 1950 2,892,743 Griest et a1 June 30, 1959 FOREIGN PATENTS 555,952 Canada Apr. 15, 1958 OTHER REFERENCES Titanium, McQuillan & McQuillan, pages 398-400, Butterworth, Scientific iublications, 1956.

Morris: Welding Principles for Engineers, page 53. 

1. A METHOD OF SURFACE-HARDENING A METAL BODY SELECTED FROM THE GORUP CONSISTING OF TITANIUM AND ZIRCONIUM, WHICH COMPRISES THE STEPS OF: FORMING A LAYER ON THE SURFACE OF THE BODY BY REACTING SAID BODY WITH A REACTIVE GASEOUS ELEMENT IN AN INERT GAS-SHIELDED ARC WELDING ARRANGEMENT BY HEATING THE BODY SURFACE TO A TEMPERATE AT WHICH IT IS MOLTEN, AND INTRODUCING IN THE INERT GAS THE REACTIVE GASEOUS ELEMENT SO THAT SAID SURFACE OF THE BODY WHILE BEING ARC-WELDING AND SHIELDED BY THE INERTG GAS, IS REACTED WITH SAID REACTIVE GASEOUS ELEMENT TO FORM THE LAYER. 